Safe Haskell | None |
---|---|
Language | Haskell2010 |
Unlifted Control.Monad.Trans.Resource.
Since: 1.1.10
Synopsis
- runResourceT :: MonadUnliftIO m => ResourceT m a -> m a
- liftResourceT :: MonadIO m => ResourceT IO a -> ResourceT m a
- data ResourceT m a
- data ReleaseKey
- class MonadIO m => MonadResource m
- register :: MonadResource m => IO () -> m ReleaseKey
- release :: MonadIO m => ReleaseKey -> m ()
- unprotect :: MonadIO m => ReleaseKey -> m (Maybe (IO ()))
- allocate :: MonadResource m => IO a -> (a -> IO ()) -> m (ReleaseKey, a)
UnliftIO variants
runResourceT :: MonadUnliftIO m => ResourceT m a -> m a #
Unlifted version of runResourceT
.
Since: 1.1.10
liftResourceT :: MonadIO m => ResourceT IO a -> ResourceT m a #
Lifted version of liftResourceT
.
Since: 1.1.10
Reexports
The Resource transformer. This transformer keeps track of all registered
actions, and calls them upon exit (via runResourceT
). Actions may be
registered via register
, or resources may be allocated atomically via
allocate
. allocate
corresponds closely to bracket
.
Releasing may be performed before exit via the release
function. This is a
highly recommended optimization, as it will ensure that scarce resources are
freed early. Note that calling release
will deregister the action, so that
a release action will only ever be called once.
Since 0.3.0
Instances
data ReleaseKey #
A lookup key for a specific release action. This value is returned by
register
and allocate
, and is passed to release
.
Since 0.3.0
class MonadIO m => MonadResource m #
A Monad
which allows for safe resource allocation. In theory, any monad
transformer stack which includes a ResourceT
can be an instance of
MonadResource
.
Note: runResourceT
has a requirement for a MonadUnliftIO m
monad,
which allows control operations to be lifted. A MonadResource
does not
have this requirement. This means that transformers such as ContT
can be
an instance of MonadResource
. However, the ContT
wrapper will need to be
unwrapped before calling runResourceT
.
Since 0.3.0
Instances
register :: MonadResource m => IO () -> m ReleaseKey #
Register some action that will be called precisely once, either when
runResourceT
is called, or when the ReleaseKey
is passed to release
.
Since 0.3.0
release :: MonadIO m => ReleaseKey -> m () #
Call a release action early, and deregister it from the list of cleanup actions to be performed.
Since 0.3.0
unprotect :: MonadIO m => ReleaseKey -> m (Maybe (IO ())) #
Unprotect resource from cleanup actions; this allows you to send resource into another resourcet process and reregister it there. It returns a release action that should be run in order to clean resource or Nothing in case if resource is already freed.
Since 0.4.5
:: MonadResource m | |
=> IO a | allocate |
-> (a -> IO ()) | free resource |
-> m (ReleaseKey, a) |
Perform some allocation, and automatically register a cleanup action.
This is almost identical to calling the allocation and then
register
ing the release action, but this properly handles masking of
asynchronous exceptions.
Since 0.3.0